I don't approve of blackballs (3)
I believe the answer is:
boo
'i don't approve' is the definition.
(expression of disapproval)
'of blackballs' is the wordplay.
I cannot quite understand how this works, but
'of' could be 'o' and 'o' is present in the answer.
The remaining letters 'bo' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for boo that I've seen before include "I disapprove" , "Sound made to show disapproval or contempt" , "Exclamation to startle" , "Shout of dislike" , "A shocking exclamation!" .)